1. Field of the Invention
The present invention relates to a method of fabricating a structure having a beam-like structure represented by a comb structure used for a sensor or an actuator fabricated by, for example, MEMS technique. The term MEMS is an abbreviation for micro electro mechanical systems.
2. Description of the Related Art
The term VC is an abbreviation for vertical comb structure. In the vertical comb structure, a pair of comb segments of a comb structure are arranged to mesh with each other, and the pair of comb segments are supported by an elastic member, for example, processed into a beam-like shape, so that one of the comb segments is displaceable outward of a plane (in a direction intersecting with a principal surface of the comb structure).
Such a structure can be fabricated as a very small structure such that, for example, a width of a single comb piece is about 5 μm, by using micro-fabrication technique to which semiconductor processing technique called MEMS is applied.
The vertical comb structure fabricated by MEMS is employed for, for example, a micro-mirror for optical-path conversion or a variable capacitor for wireless communication equipment.
For specific example, the vertical comb structure can be used as an electrode portion for an electrostatic comb actuator, in which a very small vibration structure is driven with an electrostatic force.
In the electrostatic comb actuator using the vertical comb structure, it is necessary to generate a large driving force to displace the comb structure from an initial position.
Hence, an angular vertical comb structure (AVC) and a method of fabricating the AVC are disclosed as an example of the comb structure capable of increasing the driving force (see U.S. Pat. No. 7,089,666).
FIGS. 20A to 20C show the overview of the AVC and the method of fabricating the AVC disclosed in U.S. Pat. No. 7,089,666.
The AVC disclosed in U.S. Pat. No. 7,089,666 has a structure shown in FIG. 20A.
An AVC 500 includes a movable comb segment 501 at one side of a board 503 which is supported by a torsion spring 505 and is capable of vibrating in a rotation direction.
The torsion spring 505 is made of a material, for example, monocrystalline silicon, which is plastically deformable with heat.
FIGS. 20B and 20C show a method of inclining the movable comb segment 501.
Referring to FIG. 20B, a mold 506 having a pillar 507 is pressed to the board 503 in a direction indicated by a straight arrow in the drawing such that the pillar 507 contacts an upper surface of the board 503 at a position opposite to the movable comb segment 501. Then, the board 503 is heated.
Accordingly, the board 503 rotates in a direction indicated by a curved arrow in the drawing. The torsion spring 505 is plastically deformed into a shape to keep a rotation angle of the board 503.
Then, the board 503 is cooled, and the mold 506 is detached. The board 503 is kept inclined as shown in FIG. 20C, and a comb segment 501 formed at a side surface of the board 503 is also kept inclined with the board 503.